This research is intended to evaluate quantitatively the response of microvasculature and other canine normal tissues to radiation alone, and in combination with other agents. Of specific interest are the determination of the relative biological effectiveness (RBE) of high linear energy transfer (LET) radiations, and the potential loss of capability for repair of sublethal radiation damage from high LET radiations or low LET radiations in combination with other agents. Multifraction irradiation will permit measurement of the amount of repair per fraction. Calculations of RBE for multiple fractions will be based on doses required to cause an isoeffect determined from dose response curves obtained by irradiation to variable doses given in an equal number of fractions for 60Co gamma radiation and pion or neutron irradiation. Microvascular studies will be emphasized in this work; however, response of the heart to irradiation will be evaluated, and as techniques are developed, brain and spinal cord will be included. The response of the microvasculature will be determined for single and multifraction doses of 60Co gamma radiation combined with heat, the radioprotector WR-2721 and cancer chemotherapeutic agents of interest. The response of the heart to various methods of irradiation will be compared by sequential evaluations of serum protein, serum isoenzymes, radiography, echocardiography, and electrocardiography. Morphometric analysis of the myocardium will be done. Throughout this research, efforts will be made to correlate early alterations in test values with radiation effects observed later. Some of the tests may be early indicators of late complications.